The invention relates generally to lamps and, more particularly, techniques to reduce the potential for thermal stresses and cracking in ceramic high-intensity discharge (HID) lamps.
High-intensity discharge lamps are often susceptible to crack formation and failure due to various stresses within the lamp. In certain applications, such as automotive, it is desirable to provide a quick start of the lamp. Unfortunately, this quick start subjects the lamp to severe thermal shock. For example, the quick start causes a rapid increase in temperature and hot spots within the lamp. In turn, the rapid temperature changes and hot spots (i.e., temperature differentials) often lead to the formation of cracks in the lamp. These cracks can reduce the performance of the lamp, and eventually lead to lamp failure. In addition, the liquid dose often penetrates into these cracks and further deteriorates the lamp performance and limits its life. For example, the liquid dose may be corrosive to the material (e.g., metal) in the vicinity of the cracks. These temperature differentials can have more significant effects on lamps with poorly designed geometries, interfaces, and so forth. For example, compressive or tensile stresses can develop in certain geometries and interfaces. Unfortunately, existing lamps often have geometries and/or interfaces that abruptly change, e.g., step from one diameter to another, along a length of the lamp. As a result, the severe thermal shock associated with a quick start of the lamp can lead to significantly higher stresses, hot spots, and susceptibility to cracking in the vicinity of an abrupt change in geometry and/or interfaces.